【POJ】【P2104&P2761】【题解】【区间K大】【主席树】

来源：互联网发布：c高级编程第8版中文编辑：程序博客网时间：2024/06/11 05:18

传送门：

http://poj.org/problem?id=2104

http://poj.org/problem?id=2761

裸主席树……

Code：

#include<cstdio>#include<iostream>#include<algorithm>using namespace std;const int maxn=1e5+10;int a[maxn],b[maxn];struct node{int size;node *c[2];node(){c[0]=c[1]=NULL;size=0;}void rz(){if(c[0])size+=c[0]->size;if(c[1])size+=c[1]->size;}}*Null=new node(),*root[maxn]={NULL};int tot;node poor[maxn<<4];void insert(node *&y,node *&x,int l,int r,int t){if(x==NULL)x=Null;if(tot<(maxn<<4)){y=&poor[tot++];y->c[0]=y->c[1]=Null;y->size=0;}elsey=new node();int mid=(l+r)>>1;if(l==r){*y=*x;y->size++;return;}if(t<=b[mid]){insert(y->c[0],x->c[0],l,mid,t);y->c[1]=x->c[1];y->rz();}else{insert(y->c[1],x->c[1],mid+1,r,t);y->c[0]=x->c[0];y->rz();}}int kth(node *&x,node *&y,int l,int r,int k){if(x==NULL)x=Null;if(y==NULL)y=Null;if(l==r)return b[l];int mid=(l+r)>>1;int R=0;if(y->c[0])R+=y->c[0]->size;if(x->c[0])R-=x->c[0]->size;if(R>=k)return kth(x->c[0],y->c[0],l,mid,k);else return kth(x->c[1],y->c[1],mid+1,r,k-R);}int n,m,size;int main(){Null->c[0]=Null->c[1]=Null;scanf("%d%d",&n,&m);for(int i=1;i<=n;i++){scanf("%d",&a[i]);b[i]=a[i];}sort(b+1,b+1+n);size=unique(b+1,b+1+n)-b-1;for(int i=1;i<=n;i++)insert(root[i],root[i-1],1,size,a[i]);while(m--){int l,r,k;scanf("%d%d%d",&l,&r,&k);printf("%d\n",kth(root[l-1],root[r],1,size,k));}return 0;}

新模版：

#include<cstdio>#include<iostream>#include<algorithm>using namespace std;const int maxn=1e5+10;inline int lowbit(int x){return x&(-x);}struct node{int size;node *c[2];node();void rz(){size=c[0]->size+c[1]->size;}}*Null=new node(),*root[maxn];node poor[maxn<<4];int tot;node::node(){size=0;c[0]=c[1]=Null;}int a[maxn],b[maxn];void insert(node *&y,node *&x,int l,int r,int t){//if(x==NULL)x=Null;if(tot<(maxn<<4)){y=&poor[tot++];y->size=0;y->c[0]=y->c[1]=Null;}elsey=new node();if(l==r){*y=*x;y->size++;return;}int mid=(l+r)>>1;if(t<=b[mid]){insert(y->c[0],x->c[0],l,mid,t);y->c[1]=x->c[1];y->rz();}else{insert(y->c[1],x->c[1],mid+1,r,t);y->c[0]=x->c[0];y->rz();}}int kth(node *&x,node *&y,int l,int r,int k){if(l==r)return b[l];int mid=(l+r)>>1;int R=y->c[0]->size-x->c[0]->size;if(R>=k)return kth(x->c[0],y->c[0],l,mid,k);else return kth(x->c[1],y->c[1],mid+1,r,k-R);}int n,m,size;int main(){Null->size=0;Null->c[0]=Null->c[1]=Null;  scanf("%d%d",&n,&m);  root[0]=Null;for(int i=1;i<=n;i++){root[i]=Null;scanf("%d",&a[i]);b[i]=a[i];}sort(b+1,b+1+n);size=unique(b+1,b+1+n)-b-1;for(int i=1;i<=n;i++)insert(root[i],root[i-1],1,size,a[i]);while(m--){int l,r,k;scanf("%d%d%d",&l,&r,&k);printf("%d\n",kth(root[l-1],root[r],1,size,k));}return 0;}

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